To date, it is specified in Long Term Evolution (LTE) system that PUCCH is transmitted using the fixed time-frequency resource if User Equipment (UE) has no uplink data to send. Every UE that sends control signalings in the PUCCH of the same resource block in the cell uses one control channel through code division multiplexing. As shown in FIG. 1, one control channel for one UE occupies a bandwidth of one resource block (RB) (one resource block has 12 sub-carriers) in frequency domain, and two adjacent timeslots constitute one sub-frame, that is, 1 ms in time domain. According to different cyclic prefixes used by the current sub-frame, the number of symbols within the sub-frame is different. Moreover, the control channel frequency-hops in two timeslots to obtain the diversity gain in frequency domain. Since the number of UEs that can be multiplexed in one resource block is limited, when the number of UEs which need to simultaneously send uplink control signalings through the PUCCH within the cell exceeds that of UEs that can be multiplexed in one resource block, another resource block might be opened up, that is, implementing the multiplexing of the PUCCH by each UE in a cell by a way of combination of code division and frequency division.
In the current LTE system, PUCCH is capable of supporting several types of uplink control signalings, including acknowledgement/non-acknowledgement message (ACK/NACK), channel quality indicator (CQI), scheduling request (SR), or their combinations, that is, several types of uplink control signalings are sent simultaneously, wherein, ACK/NACK and SR are sent in the control channel format 1 and CQI is sent in control channel Format 2. All kinds of PUCCHs are described briefly in the following.
As shown in FIG. 2, ACK/NACK is BPSK (binary phase shift keying) or QPSK (quadrature phase shift keying) modulated to form a modulation symbol, and the modulation symbol is spectrum spread with spreading factor of 12 in frequency domain, wherein the spread spectrum sequence is a CAZAC (constant amplitude zero auto correlation) sequence whose length is 12, and then the modulation symbol is spread with a Walsh code whose length is 4 in time domain and then mapped to the information symbol corresponding to the control channel format 1 shown in FIG. 2 (wherein denotes the information symbol and  denotes the pilot frequency symbol, namely, the reference signal), that is to say, l=0, 1, 5, 6, where l is the index of the symbol.
The reference signal, mainly used as the channel estimation of the information symbol carries no information and is processed the same as the information symbol, that is, spectrum spread with the spreading factor of 12 in frequency domain, and then spread with an orthogonal sequence whose length is 3 (normal cyclic prefix) or 2 (extended cyclic prefix) in time domain, and finally, the reference signal along with the ACK/NACK information symbol constitutes a signal for sending in one timeslot. Therefore, the number of UEs multiplexed to simultaneously send ACK/NACK in one resource block is determined by the number of the relatively short orthogonal codes in time domain and the cyclic shifts of the CAZAC sequence allowed using in the same orthogonal code. The number of relatively short orthogonal codes in time domain is 3 when the cyclic prefix is the normal cyclic prefix and 2 when it is the extended cyclic prefix, while the cyclic shifts of the CAZAC sequence allowed to use in the same orthogonal code depends on the application scenarios. Generally, the ACK/NACK channel can be represented by the combination of the cyclic shift (CS) of the CAZAC sequence used by the channel and the corresponding index of the orthogonal code (OC) in time domain, that is, CB=<OC, CS>.
As shown in FIG. 3, CQI is encoded into 20 bits, and then QPSK modulated into 10 modulated symbols S0˜S9, each modulated symbol is spectrum spread with a spreading factor of 12 in frequency domain (and the spread spectrum sequence is a CAZAC sequence with the length of 12), and then mapped to the information symbol corresponding to the control channel format 2 shown in FIG. 3. The role of the reference signal is the same as that of ACK/NACK, after being spectrum spread with a spreading factor of 12 in frequency domain, the reference signal along with the CQI constitutes a signal for sending in one timeslot. Therefore, in one resource block, the number of UEs multiplexed to simultaneously send CQI is determined by the number of the cyclic shifts of the CAZAC sequence allowed to use. Generally, CQI channel may be represented by the cyclic shift (CS) of the CAZAC sequence used by the channel.
In general, the UEs sending ACK/NACK and those sending CQI use different resource blocks to send their corresponding uplink control signalings, LTE also supports that ACK/NACK and CQI of different UEs are sent in the same resource block at present, and it is specified that there is only one such resource block at most, and it is called “the mixed resource block”.
Normally, different cells are allocated with different CAZAC root sequences as their spectrum spreading sequences, while the control channel of each UE in the cell uses different cyclic shifts of the same CAZAC sequence. Since the correlation of different cyclic shifts of different CAZAC root sequences is different, the cyclic shifts of the CAZAC sequences used in each symbol in uplink control channel is different in order to make the interference among the cells randomized, that is, the cyclic shifts of the CAZAC sequence corresponding to each symbol hops as time, and the hopping pattern is cell-specific (the hopping patterns of all UEs in the cell are the same), that is, in the symbols whose timeslot number and the time domain number are the same, the interval of cyclic shifts of the sequence used by every two UEs is the same for all the UEs in the cell.
In addition, in order to further improve the performance of uplink control channel, intra-cell interference randomization should be taken into account. From the above content, it can be seen that the control channel of each UE which sends uplink control signaling in the PUCCH of one resource block in the cell is code division multiplexed, and in the ideal channel, the control channel of each UE in the cell is ideally orthogonal, in the practical channel however, the orthogonality of the control channel of each UE is damaged due to the channel fading delay and the Doppler shift because of the moving of UE, therefore, the control channels of the UEs in the cell are interfered with each other. For different uplink control channels, their interference is different. For ACK/NACK channel, the damage of orthogonality comes from two sides, on one side, the orthogonality of the CAZAC sequence in frequency domain is damaged due to the channel time delay spread, moreover the orthogonality is related to the difference of the cyclic shift of the CAZAC sequence used, for instance, the orthogonality is relatively poor in the delay fading channel when the difference of the cyclic shift is relatively small, such as the adjacent cyclic shifts, while maintains well when the cyclic shifts have relatively large interval; on the other side, the orthogonal codes in time domain are damaged due to the Doppler shift and the damage degree is related to the moving speed of UE. For CQI channel, the reason of the damage to the orthogonality is that the orthogonality of CAZAC sequence in frequency domain is damaged because of the time delay spread of the channel.
As mentioned above, since the hopping patterns of cyclic shifts of CAZAC sequence are cell-specific, that is, the hopping patterns of all UEs in the cell are the same, therefore, if two UEs use control channels which interfere with each other severely, the interference in the sustained period of control channel is relatively severe.